INDIANAPOLIS — As the Giants came onto the field for the third quarter of Super Bowl XLVI last night, Deon Grant and Mario Manningham had a chat.

“He was down because he had got one catch the first half. And he was telling me, ‘D, say a prayer for me because I need to get involved in this game to help our team out,’ ” Grant said. “I said, ‘What God has for you is meant for you.’ I said, ‘You just make sure you prepare when that ball comes to you. Because it’s gonna come to you the second half.’ ”

It did. And Manningham was prepared. In the Giants’ 21-17 win over the Patriots, the Giants wideout — at times overshadowed this season — delivered a mesmerizing catch to start off his team’s final game-winning drive.

On the Giants’ first play of the drive, with 3:46 to go and the team on its 12-yard line, Eli Manning heaved a deep pass down the Patriots sideline. Manningham, covered by Sterling Moore and Patrick Chung, hauled it in with an incredible grab, keeping both feet in bounds for a 38-yard gain to midfield.

“That was the turning point,” Hakeem Nicks said.

The Patriots challenged the completion, but it was upheld and Giants fans exploded when the replay showed it was legit.

“He had both feet down. Good throw, good catch,” Chung said.

Manningham said, “I knew I had my feet in,” Manningham said, “but I just didn’t know if the refs were going to try some funny stuff.”

The catch put the Giants at midfield, and they took the lead with 57 seconds left on Ahmad Bradshaw’s six-yard touchdown scamper. Thanks in large part to Manningham. Said Tom Brady: “That got them going.”

Manningham’s mother, Marion — sporting her son’s jersey — was asked if this was Mario’s best catch ever. She raved about a grab he had back in high school, but admitted last night’s topped it.

“It is the Super Bowl. I’m gonna give this one a 10, ’cause it counted. The other one was a nine,” she said. “This is the best. This is the best.”

Manningham ended up catching passes on the next two plays of the drive too, one for 16 yards and one for two yards. He finished his first Super Bowl with five catches for 73 yards, capping a superb postseason for him — Manningham had touchdown catches in the Giants’ first three playoff games, and the free-agent-to-be certainly showcased his value with his postseason.

Manningham may be a longshot to be back, since the Giants also have Nicks and Victor Cruz, who need to be signed to extensions. He dismissed a question about his free agency in postgame.

“I don’t want to talk about that,” he said. “I want to enjoy this win.”

He also didn’t want to compare his catch to David Tyree’s in Super Bowl XLII, explaining that he didn’t catch it crazily like Tyree did.

“It was just a catch,” Manningham said. “We work on that all the time. The sideline catch, the fade. We work on our footwork all the time.”